Physiology of pregnancy Flashcards
Increase in physiological demands for the foetus
Nutrients (O2, amino acids, glucose)
Amniotic fluid production
Removal of foetal waste products (CO2, nitrogen compounds)
Requires increased
- nutrient content (GI)
- oxygen content (pulmonary and CV)
Volume homeostasis
A rpaid increase in plasma volume by 40%
- 2.5L to 3.7L by end of pregnancy
- 11-13kg weight gain
Plasma colloid osmotic pressure falls
- causes a shift of fluid into extra cellular space
- increased hydration of connective tissue
- oedema (lower limbs, hands and face)
Mechanisms in increased plasma volume
Slight decrease ANP
Decreased thirst threshold (increased fluid intake)
Re-setting osmostat
Increased plasma volume
Red blood cells
Haemoglobin
- red cell mass increased by 25%
- plasma volume increased by 40%
- 13.3 to 10.9g/dL at 36 weeks
- dilutional anaemia
Iron is required for the increased red cell mass
- fall in ferritin levels
- increased iron absorption from gut
No need for routine Fe supplementation except for twins
Delivery of blood to the uterus; uterine artery blood flow increases 3.5 fold from 95 to 342 ml/min
Hypercoagulable state
Increase plama fibrinogen, platelets, factors VIII and von willebrand factor
Evolutionary balance between thrombosis and haemorrhage
White blood cells
Concentration does not fall during pregnancy
Total WBC increases in pregnancy
Increase in neutrophil s (reduced apoptosis)
Marked increases around delivery
Cardiovascular system
Increases blood volume has implications on:
- cardiac output
- peripheral resistance
- blood pressure
Heart changes
Heart enlarges by 12% (increased venous return)
Innocent systolic murmurs are common (90%)
Diastolic murmurs (20%) require investigation to rule out pathologies
- may be innocent
- rule out cardiopathies
Peripheral resistance
Peripheral vasodilation (effect of progesterone)
Peripheral resistance decreases by 35%
Blood pressure
Decrease resistance partly compensated by increase in cardiac output
Results in small change in BP
Respiratory system
Increased pulmonary blood flow matched by increase tidal flow
Decreased maternal pCO2 and increase maternal pO2
Increase availability of O2 to tissues and aids passive diffusion at the placenta i.e. higher concentration gradient
Effects of CV and resp changes
High blood flow maximises pO2 on maternal side of the placenta
Foetal haemoglobin has a higher affinity for O2 compared with maternal adult Hb
Increased cardiac output may increase flow in skin aiding heat loss
Renal system GFR and reabsorption
Kidney increases 1cm in size during normal pregnancy
GFR and effective renal plasma flow increases 50+%
Tubular reabsorption capacity is unchanged
- leads to a decrease in glucose reabsorption thus glycosuria is common
Renal system
Plasma levels of creatinine and urea decrease in pregnancy
All the increments are present by the second trimester
Reduction in GFR of 15% during the third trimester
Dilation of renal pelvis and ureters (progesterone)- increased urinary tract infection in pregnancy
Gastrointestinal system
Gastro- oesophogeal reflux up to 70%
- due to increase in abdominal pressure, reduced pyloric sphincter with back wash of bile secondary to hormonal changes
- simple measures: avoidance of fat and alcohol
- upright posture and antacids
Slowing of gut motility and constipation (progesterone effect)
